(1) Field of the Invention
The present invention relates to optical fiber-containing insulators in which an optical fiber is buried to transmit signals from a power transmission line to a ground contact side.
(2) Related Art Statement
As disclosed in Japanese patent application Laid-open No. 60-158,402, there have formerly been known optical fiber-containing insulators in which a through hole of a small diameter is formed in an axial portion of an insulator body and an optical fiber is passed through the through hole, while an insulating material such as an epoxy resin is filled between the inner peripheral surface of the through hole and the optical fiber. The insulating material filled has important roles in preventing a leakage current from flowing along the optical fiber and preventing decrease in a surface leakage-insulating distance of the insulator. When the insulator is subjected to high temperatures, the insulating material such as epoxy resin is greatly forced out from the insulator body in an axial direction thereof due to great difference in coefficient of thermal expansion between the porcelain and the insulating material so that a tension acts upon the optical fiber and that adhesion between the insulating material and the insulator body is lost. Consequently, it is feared that penetrating voltage resistance of the insulator is greatly lowered.
Further, since the through hole is long and small in diameter, it is difficult to accurately hold the optical fiber in the center of the through hole so that there is the possibility that the optical fiber partially touches the inner peripheral wall of the through hole. Since no insulating material is present between the optical fiber and the inner peripheral wall of the through hole there, adhesion is lost at that portion so that water or moisture is likely to enter to lower electric insulation performance.